The present invention relates generally to thin film resistors and pertains particularly to controlled temperature coefficient of resistance thin film resistors and method of making same.
Thin film technology is utilized in the production of micro circuits. The materials produced by the thin film technology frequently have properties different from the same materials in bulk compositions. Accordingly it has been found that bulk or thick film technology cannot be readily adapted to thin film technology.
In the past, thin film resistors have been made from a number of compositions. The primary technique of thin film resistor construction utilizes tantalum, refractory metal oxides, and nickel chromium alloys. Perhaps the most commonly used material at present is that of an alloy of nickel-chromium.
Resistors made of this composition typically have a temperature coefficient of resistance (TCR) which generally runs around 40 to 200 ppm/degree centigrade. While thin film resistors of these materials are satisfactory for many applications, they are unsatisfactory for certain specific advanced applications. The TCR is especially critical in certain micro circuits which are necessarily subjected to extreme environmental conditions. Because of the environmental conditions encountered it is desirable to be able to tailor the circuit to the conditions expected. For example, extreme temperatures can affect the performance of the circuit. It is desirable that the circuit be balanced for the respective temperatures encountered.
It is therefore desirable that thin film resistors and method of making such resistors be available for tailoring the TCR to meet certain requirements.